This invention relates to a method by which the capacitance of aluminum electrolytic capacitor foil is increased by treating the foil prior to anodization with boiling water and then with a boiling aqueous solution containing phosphate, silicate, or tartrate ions, or combinations thereof.
It is known that hydrous oxide films can be formed on aluminum by treating the foil with boiling water and that anodization after such treatment consumes less charge than does anodization of untreated foil. Furthermore, the film formed thereby has significantly higher capacitance than a normal barrier oxide film formed on untreated aluminum.
Several of the additives claimed have usefulness in the capacitor industry for a variety of other purposes such as passivation of capacitor foils, removal of impurities, stripping of excess hydrate, protection against effects of moisture, etc., among them phosphates, silicates, and tartrates.